A known device restricts engine output when a drive power output system for an internal combustion engine has an abnormality. For example, patent document 1 discloses a device that lowers the engine output by restricting fuel injection amounts when there is an abnormality to enable a vehicle evacuation travel while protecting the internal combustion engine.    Patent Document 1: Japanese Laid-Open Patent Publication No. 10-159620 (pp. 4 to 5, FIG. 2).
However, in the output restriction device disclosed in patent document 1, when there is an abnormality in the drive power output system, the output of the internal combustion engine decreases suddenly as the operation state of the internal combustion engine shifts to a state enabling the vehicle evacuation travel. Thus, if an abnormality is detected in an internal combustion engine mounted on a vehicle when the vehicle is being accelerated in an overtake lane, the driver may feel greatly uncomfortable since the output greatly decreases even though the driver is accelerating the vehicle.
To solve this problem, the output may be restricted in a manner that it does not greatly decrease when there is an abnormality. In this case, however, an output state that is not suitable for the internal combustion engine may continue for a long period depending on how the driver operates the vehicle. Continuation of such an unsuitable state over a long period may further advance the abnormality such that the internal combustion engine cannot continue to operate. As a result, the vehicle may not be able to complete the evacuation travel.